Condensation reaction between urea and formaldehyde has been known for many years. Urea formaldehyde based insulation foams have been commercially available in the United States since at least as early as the 1950's. They were, however, at that time not widely used. In recent times, with the emphasis on energy conservation, there has been an increasingly greater use of these materials for residential insulation, and in particular, as a foamed insulation to be used in wall spaces and the like, of existing building structures.
With the increasing use of urea formaldehyde foamed insulation to increase insulating capacity, there has been concern expressed about off-gassing of formaldehyde from the insulation, after installation. It appears that temperature and humidity affect the levels of formaldehyde off-gassing. Also, there appear to be two emission phenomena occurring. The first involves a short term release of formaldehyde and the second involves a lower level, long term release.
The release of formaldehyde from the resin into the interior of a dwelling structure is undesirable. It has been linked with certain physical and biological effects. This is particularly true for low level, long term release of out-gassed formaldehyde which may expose persons inside of the insulated dwelling to potential long term risks. In fact, because of such concerns, urea formaldehyde foamed insulation has recently been banned for use in the United States.
Thus, while urea formaldehyde foamed insulations unquestionably are effective from the insulating standpoint, if they are to be used in the future, there is a real and continuing need for developing such a foamed insulation which will eliminate or minimize the out-gassing of formaldehyde, both from the standpoint of short term release and most importantly, from the standpoint of the lower level, long term gradual release.
Urea formaldehyde resins are a mixture of products from the condensation reaction between urea and formaldehyde. The first stage of the condensation is commonly carried out at 70.degree. to 100.degree. C. with a urea formaldehyde ratio of approximately 1.5 and a pH of from about 4 to about 8. This results in a mixture of mono and di-methylol urea. The product of this first condensation takes on a variety of forms which are dependent upon reaction conditions such as pH, temperature and the mole ratio of urea to formaldehyde. They can be prepared as syrupy, aqueous solutions, water soluble fine grain powders, or water insoluble materials which precipitate from the reaction solution. The urea formaldehyde resin mixture previously described is used for the production of urea formaldehyde foam insulation.
Three major components are necessary for production of the final foamed product, which is generated on site using portable equipment. The components are a partially polymerized urea formaldehyde resin, a foaming agent and air or nitrogen. Typically, the resin is an aqueous solution of a precondensate urea formaldehyde resin. The foaming agent is a surfactant which contains an acid catalyst or hardening agent, and the last component is air or nitrogen. The resin and the surfactant-catalyst are both water solutions. Naphthalene sulfonic acid and dodecyl benzene sulfonic acid have been used as foaming agents and phosphoric, oxalic, citric, malic, and tartaric acids have been used as the acid catalyst.
In general, generation of the foam insulation requires the use of compressed gas and a mixing or foaming gun. The process involves two events which consecutively take place in the gun. The first component comprising an aqueous solution of the foaming agent-catalyst mixture is pumped into the gun where compressed air mixes with it to form a foam of small detergent bubbles. Subsequently, the bubbles are coated in the nozzle of the gun by the urea formaldehyde resin component which is supplied from a separate line. The resin coated bubbles are forced out of the gun under pressure which results in a white foam resembling shaving cream. The resin, after mixing with the catalyst at the surface of the bubbles, begins to polymerize (cure) and within less than a minute, the resin has partially cured into a stiff, self-supporting foam.
The product as it exits from the gun is injected into the interior wall space for insulation in a dwelling. Commonly, it is injected through holes in the outer wall structure, or it may be troweled from inside before dry wall is added. Foam has also been used as insulation by filling the cavities in cinder block or in buildings.
As heretofore mentioned, a latent and intrinsic property of urea formaldehyde resin based insulation is the release of formaldehyde. This is magnified in homes using urea formaldehyde resin since a large surface area is involved, which can slowly release formaldehyde, particularly if exposed to moisture or if the resin is not properly cured. Moisture problems can cause serious effects at high humidity since this will cause hydrolysis of urea formaldehyde resins in the presence of acids used during the formation of the foam which in turn results in liberation of formaldehyde.
The specific details of forming the urea formaldehyde foam and inserting it into a building structure, are well known and do not form a part of this invention. For further information on such details, see Beat-Meyer, Urea Formaldehyde Foamed Resins, Addison Wesley Publishing Company, Inc. 1979, pages 185-198, which are incorporated herein by reference.
It is thus apparent that the primary objective of the present invention is to prevent urea formaldehyde off-gassing or release of formaldehyde after foaming and insulating, all in the hope that the recent ban of sales of such in the United States can be lifted, and that this highly effective insulation can once again be used.